1. Field of the Invention
The present invention relates to a solder precipitating composition suitable for soldering electronic components and a method of precipitating a solder by using the same.
2. Description of the Related Art
A surface mounting technology for electronic components has been widely employed in order to manufacture light, thin, and compact electronic devices. According to this technology, a solder cream is applied to a pad of a printed circuit board, and each electronic component is placed thereon. The circuit board with the electronic components is placed in a reflow furnace to melt the solder cream, thereby soldering the leads of the electronic components to the pads of the printed circuit board.
A solder cream used in this technology is prepared by dispersing a solder alloy powder and a flux in a high-boiling point solvent such as a mineral spirit to impart a predetermined viscosity to the solder cream.
A method using the solder cream can be applied to a wiring pattern having a lead pitch of about 0.65 mm. However, this method cannot be applied to smaller wiring patterns because of the fact that bridges (i.e., conduction between the pads through the solder) tend to be formed. This method cannot cope with the trend of a higher integration density of electronic circuits.
In order to solve the above problem, an organic solder is proposed wherein tin or lead is bonded to a maleic or fumaric adduct of rosin, and a metal component is eliminated upon heating to precipitate a solder (Japanese Patent Application No. 61-72044). However, in order to increase the metal content, this organic solder is prepared such that rosin is converted into a maleic or fumaric adduct to introduce a carboxylic acid, and tin or lead is introduced into the carboxylic acid. Therefore, solubility of the resultant organic solder in organic solvents is poor. For this reason, it is difficult to control the viscosity of the organic solder and to apply it to a wiring micropattern.